1. Field of the Invention
The present invention relates to a plating device for applying a bump-plating treatment to wafers as one of the steps in the process for producing a semiconductor.
2. Description of the Prior Art
Bump-plating of a wafer is generally carried out by bringing the wafer immobilized as pressed onto the mounting surface around the opening of a cup-like plating tank into contact with a plating solution contained in the plating tank (e.g. as disclosed in Japanese Utility Model Laid-Open Publication Nos. Hei 2-38472 and Hei 2-122067, or Japanese Patent Laid-Open Publication No. Hei 5-320978).
Such plating treatment of the wafers involves some problems, and one of them is how to secure electrical continuity between the wafer, especially one which must be charged from the surface thereof on which a resist film is formed, and the cathode. In one of the measures to solve such problems, the resist film formed on the surface of the wafer is pierced with the sharp point of a needle-like electrode to be penetrated thereby when the wafer is immobilized as pressed onto the mount. This method involves problems that the adjustment of the height of the electrode is difficult, and that if a plurality of needle-like electrodes are provided, unstable contact of the needle-like electrodes is caused due to the nonuniform height thereof, etc. (e.g. as described Line 3, Page 4 to Line 1, Page 5 of Japanese Utility Model Laid-Open Publication No. Hei 2-38472).
Similar technique which also employs needle-like electrodes is disclosed, for example, in Japanese Utility Model Laid-Open Publication No. Sho 58-19170, which has overcome the problem of such nonuniform height of electrodes. According to this technique, each of the needle-like electrodes, the point of which is crooked upward, is allowed to protrude inward from the wall surface of a plating tank like a cantilever. This cantilever structure imparts elasticity to the electrode to enable absorption of unevenness in the height of the needle-like electrodes. However, no consideration is taken for the liquid tightness of the needle-like electrode against the plating solution in this structure, so that there remains an inconvenience that the plating metal deposits on the exposed portion of the needle-like electrode.
There is another technique in which a plate-like electrode is pressed against a wafer via a conductive buffer plate, as disclosed in Japanese Utility Model Laid-Open Publication No. Hei 2-38472. This method, although it can overcome the problems inherent in the technique using needle-like electrodes, involves other problems. Namely, the resist film present over the range to be pressed against the electrode must preliminarily be removed in this method to increase the number of steps; the yield is affected, since more than a predetermined width of the resist film must actually be removed over the entire periphery of the wafer; and so forth.